Re: Estimating HugePages Requirements?

On Fri, Aug 27, 2021 at 8:46 AM Michael Paquier <michael(at)paquier(dot)xyz> wrote:
>
> On Wed, Aug 11, 2021 at 11:23:52PM +0000, Bossart, Nathan wrote:
> > I think BootstrapModeMain() makes the most sense. It fits in nicely
> > with the --check logic that's already there. With v3, the following
> > command can be used to retrieve the amount of shared memory required.
> >
> > postgres --output-shmem -D dir
> >
> > While testing this new option, I noticed that you can achieve similar
> > results today with the following command, although this one will
> > actually try to create the shared memory, too.
>
> That may not be the best option.

I would say that can be a disastrous option.

First of all it would probably not work if you already have something
running -- especially when using huge pages. And if it does work, in
that or other scenarios, it can potentially have significant impact on
a running cluster to suddenly allocate many GB of more memory...

> > IMO the new option is still handy, but I can see the argument that it
> > might not be necessary.
>
> A separate option looks handy. Wouldn't it be better to document it
> in postgres-ref.sgml then?

I'd say a lot more than just handy. I don't think the workaround is
really all that useful.

(haven't looked at the actual patch yet, just commenting on the principle)

--
Magnus Hagander
Me: https://www.hagander.net/
Work: https://www.redpill-linpro.com/